The invention relates to a vacuum tube provided with at least one semiconductor cathode having an emissive surface for emitting electrons and an electron-optical system comprising a plurality of grids of a conducting material.
An emissive surface can herein also be understood to mean a main surface on which one or more punctiform emitters or field emitters are arranged or in which pits are provided from which the emission takes place.
The invention also relates to a method of manufacturing such an electron-optical system and to a method of securing this system in a vacuum tube.
A vacuum tube in which an electron beam is deflected through an angle of 90.degree. over a very short distance (several mm) is proposed in the simultaneously filed application Ser. No. 156,491. Such a deflection cannot be realized with the conventional techniques.
It is an object of the invention to realise this possibility and to indicate measures with which an electron-optical system of very small dimensions can be manufactured, even if the said deflection is not strictly necessary.